In-Situ Measurements of Unsteady Hydrodynamic Forces on a Solid Boundary Using Strain-Gage Based Transducers

This research aims to develop an apparatus to achieve in-situ measurement of unsteady hydro-dynamic forces. The current facility has been built by integrating sensing modules, a motion control system and a data acquisition system. Two types of sensing modules have been developed using conventional strain gages for shear stress measurement and transducers for pressure measurement individually.

Extensive efforts were made to calibrate the sensing modules using well-controlled fluid mo-tions. For shear stress sensing modules, steady and quasi-steady test were performed using a rota-tional Couette flow and an oscillating flow as described in the Stokes second problem. Theoretical analysis has also been conducted to examine the experimental findings. It was found that the sens-ing module for shear stress measurement responds to both the viscous stress and the thermal inter-actions with the flow.

For pressure sensing modules, a quasi-steady test was performed using a vertical oscillation. Based on the proposed working formula, we gave predictions to the instantaneous dynamic pressure and compared it with the actual measurements.